The present invention relates to a process for preparing a heterometallic oxide film of the LIMO2 type, wherein M is a Group 13 element such as Al or Ga, using a volatile organometallic compound of formula LiORxe2x80x2.(Rxe2x80x2O)MR2 wherein R is a C1-10 alkyl group; and Rxe2x80x2 is a C2-10 alkyl group.
Theoretical and experimental studies have projected that a heterometallic oxide of the LiMO2 type, e.g., LiAlO2 and LiGaO2 would be useful in a process for depositing a blue luminescent GaN film thereon because its lattice constant (a-axis) is almost identical with that of GaN (Nicholls, J. F. H. et al., xe2x80x9cGrowth and optical properties of GaN grown by MBE on novel lattice-matched oxide substratesxe2x80x9d in Gallium Nitride and Related Materials; and Ponce, F. A. et al., eds. Materials Research Society Symposium Proceedings, 395, pp. 535-539 (Materials Research Society, Pittsburgh, Pa., USA, 1990)).
From these studies, it is thought that films of LiO2 type grown on Si wafers should be useful as buffer layer for the deposition of GaN films.
Despite such anticipated usefulness, a LiMO2 film has not been successfully prepared in the past due mainly to the lack of suitable organometallic precursor compounds that can be used in the chemical vapor deposition (CVD) process for preparing a LiMO2 type oxide.
Accordingly, there has existed a need to develop a scheme for the preparation of such precursor compounds.
Accordingly, it is an object of the present invention to provide a process for preparing a heterometallic oxide film of the LiMO2 type, wherein M is a Group 13 element.
In accordance with one aspect of the present invention, there is provided a process for preparing said film which comprises contacting the vapor of a volatile organometallic compound of formula LiORxe2x80x2.(Rxe2x80x2O)MR2 with a substrate heated to a temperature above 300xc2x0 C., wherein M is a Group 13 element; R is a C1-10 alkyl group; and Rxe2x80x2 is a C2-10 alkyl group.
The organometallic compound which may be used in the present invention is a highly volatile compound of formula LiORxe2x80x2.(Rxe2x80x2O)MR2 which has a Li:M:O atomic ratio of 1:1:2. It can be, therefore, advantageously used in a CVD process for depositing a LiMO2 type heterometallic oxide film on a substrate. In the organometallic compound of formula LiORxe2x80x2.(Rxe2x80x2O)MR2, M is a Group 13 element such as Al or Ga; R is a C1-10 alkyl group; and Rxe2x80x2 is a C2-10 alkyl group. The preferred compounds in practicing the present invention are lithium dimethylaluminum isopropoxide, LiOPri.(PriO)AlMe2; lithium dimethylaluminum tert-butoxide, LiOBut.(ButO)AlMe2; and lithium dimethylgallium isopropoxide, LiOPri.(PriO)GaMe2.
The organometallic compound may be prepared according to the process described in WO 97/29112 or in U.S. Pat. No. 6,063,951. That is, a dialkylmetal alkoxide((Rxe2x80x2O)MR2) may be directly reacted with a lithium alkoxide(Li(ORxe2x80x2)) in a molar ratio of 1:1 to obtain the desired product, as shown below:
LiORxe2x80x2+(Rxe2x80x2O)MR2xe2x86x92LiORxe2x80x2.(Rxe2x80x2O)MR2 
wherein M, R and Rxe2x80x2 have the same meanings as defined above.
The organometallic compound thus obtained may be preferably vaporized at a temperature ranging from room temperature to 100xc2x0 C.
A heterometallic oxide film of the LiMO2 type may be deposited on a substrate by bringing the vapor of the organometallic compound thus obtained into contact with the surface of the substrate preheated to a temperature above 300xc2x0 C., preferably from 300xc2x0 C. to 600xc2x0 C. under a pressure of from 7.5xc3x9710xe2x88x926 to 1.5xc3x9710xe2x88x922 Torr., preferably under a pressure ranging from 5xc3x9710xe2x88x923 to 1.2xc3x9710xe2x88x922 Torr.
The substrate which may be used in practicing the present invention is any inorganic solid which is stable at or above the film deposition temperature, and examples thereof include: glass, quartz, silicon, gallium arsenide, sapphire, alkali metal niobate, alkaline earth metal titanate, gallium nitride, niobium nitride and the like. Among those, single crystals of silicon, gallium arsenide and sapphire are preferred when the coated substrate is intended for use in electronic applications.
The following Preparation Examples and Examples are provided only for the purpose of illustrating certain aspects of the present invention; and they are not to be construed as limiting the scope of the present invention in any way.
In each of Examples, the coated substrate obtained after treatment with an organometallic compound was immediately transferred to an X-ray photoelectron spectroscope in order to minimize its exposure to air.